I. Field of the Invention
This invention relates to molten metal containment structures used for conveying, treating or holding molten metals, incorporating refractory or ceramic molten metal containment vessels, such as troughs or crucibles. More particularly, the invention relates to the provision of covers for such structures and vessels.
II. Background Art
Molten metal containment structures, e.g. metal-conveying troughs or launders, are often required during metal treatment or casting operations to convey molten metal from one location, such as a metal melting furnace, to another location, such as a casting mold or casting table. In other operations, such vessels are used for metal treatments, such as metal filtering, metal degassing or metal transportation.
When the vessels contained in such structures are open at the top, it is desirable to provide a cover both to keep heat in and to keep foreign objects and debris out. Sometimes, such a cover is provided with heaters to heat the vessel in advance of molten metal entry, or to maintain the high temperature of the molten metal as it is being treated or conveyed. It is desirable to make such covers removable so that operators may obtain access to the interior of the vessel, e.g. to clean out the vessel, to remove blockages or to assess molten metal height or condition. The covers may be loose, thereby requiring the operator to lift and move the covers manually, or they may be attached to the structure by hinges typically on the side of the vessel most distant from the operator.
A disadvantage of providing such removable or openable covers is that their undersides, i.e. the surfaces facing the molten metal, become very hot in use and operators of the equipment may be exposed to heat radiating from the undersides when the covers are lifted, resulting in discomfort or burns. In operation with molten aluminum alloys, for example, the underside of a cover may have a temperature within the range of 400 to 800° C. when raised. Moreover, a simple hinge may result in crowding of the opening by the cover, even when the cover is fully retracted. Covers of this kind are often made of a metal shell with a refractory lining and may incorporate heaters of one kind or another. As a result, such covers can be quite heavy, so the lifting may be difficult when attempted by hand, and damage may be caused (particularly to integral heaters) if the covers are simply allowed to fall back into place.
An example of a known metal-conveying trough provided with a cover is disclosed in U.S. Pat. No. 4,531,717 which issued to Georges Hebrant on Jul. 30, 1985. The elongated trough is provided with a number of covers attached to the trough by hinges. The covers are provided with heating means to pre-heat the trough. The force required to open the covers is somewhat reduced by springs which tend to urge the cover to the open (raised) position. However, the operator is exposed directly to the hot underside of the cover when the cover is raised.
Another example of a known device is disclosed in U.S. patent publication 2008/0230965 A1, which was published on Sep. 25, 2008 naming Robert Gorza, et al., as inventors. This publication discloses a floor-mounted handling device, which is a kind of small crane, for removing covers from metal conveying troughs and runners. The device can handle covers of virtually any weight and avoids exposing operators to hot environments. However, the apparatus is costly and requires clear floor space around the troughs or runners.
There is a need for additional approaches for addressing some or all of the problems mentioned above.